Monitoring Sprinkler Irrigated Wheat and Camelina Canopy Temperatures With a Wireless Sensor Network.

Wireless sensor networks have the potential to provide low-cost, time continuous plant canopy surface temperatures for estimating the spatial distribution of evapotranspiration (ET) over crops. These temperatures, when combined with meteorological observations, can be used to constrain the surface energy balance and detect plant water stress. However, the temperature data from these networks are point-based observations that may not be representative of field-wide conditions and thus could lead to large ET estimation errors. To evaluate ET uncertainties modeled for wireless sensor network temperatures, a study over wheat and camelina was conducted in 2012 at Maricopa, Arizona. The crops were sprinkler irrigated in an unusual water-gradient design, which allowed parallel development of increasing amounts of plant water stress with good constraints on water inputs.  Ten wireless sensor nodes monitoring plant temperatures across the irrigation gradient were deployed. Air temperature and humidity were also monitored with the network. In tandem with these observations, soil moisture profile data were logged continuously, while frequent agronomic data over both crops were collected.  Wireless temperature sensors showed strong correspondence between canopy temperatures and irrigation gradients, while ET estimates derived from these temperatures agreed well with observed soil moisture depletions. These findings and their field-wide extension will be discussed.